This invention relates to a feathering propeller, and more particularly to a feathering propeller for auxiliary engines of sailing boats.
As is well known to all those concerned with sailing, the engine, and the propeller driven by it, are used only exceptionally, for example for manoeuvres in ports or in cases of emergency, and they are required to disturb running under sail as little as possible. In particular, the propeller must offer the minimum possible resistance to the water when not in use, while remaining in position and touched by the relative water current. Three types of propellers are used at present, namely:
FIXED
CLOSABLE (OR BEAK TYPE), AND
FEATHERING.
The fixed propeller offers high hydrodynamic resistance because of the fierce vortices which it creates in the water.
The closable propeller however offers a much smaller resistance because it does not create vortices when the blades are closed.
This type of propeller is the type most frequently used at present. However, reversing with this propeller is difficult and inefficient.
The feathering propeller is the least used at present, because the embodiments constructed up to the present time have two main disadvantages:
(A) THEY CREATE VORTICES IN THE WATER DUE TO THE CURVATURE OF THE BLADE SURFACES, EVEN WHEN THE BLADES ARE FEATHERED.
(B) THEY ARE MECHANICALLY COMPLICATED (THEY OFTEN COMPRISE PITCH VARIATION CONTROLS INSIDE THE DRIVE SHAFT).
In calculating the rating, account is taken of the hydrodynamic resistance offered by these three types of propeller by attributing three different coefficients to them. The rating is notably a decisive factor in the chances of victory of a sailing boat in a regatta. A favourable rating therefore considerably increases the value of the boat itself.
The rating coefficient for the feathering propeller is more favourable than that for the closable propeller, because the rules have been drawn up in such a manner as to compensate for the disadvantages of the present feathering propellers described heretofore (points a and b).